Multistage process for the polymerization of olefins

Abstract

A process for polymerizing olefins at temperatures of from 30° C. to 140° C. and pressures of from 1.0 MPa to 10 MPa in the presence of a polymerization catalyst in a multistage polymerization of olefins in at least two serially connected gas-phase polymerization reactors, and apparatus for the multistage polymerization of olefins, comprising at least two serially connected gas-phase polymerization reactors and a device for transferring polyolefin particles from an up-stream gas-phase polymerization reactor to a downstream gas-phase polymerization reactor, the transferring device comprising—a gas/solid separation chamber placed downstream of the upstream gas-phase polymerization which gas/solid separation chamber is equipped at a lower part with an net for introducing a fluid, and—connected to the gas/solid separation chamber at least two lock hoppers, placed in a parallel arrangement, each connected to the downstream gas-phase polymerization reactor.

The invention claimed is: 
     
       1. A process for polymerizing olefins at temperatures of from 30° C. to 140° C. and pressures of from 1.0 MPa to 10 MPa in the presence of a polymerization catalyst in a multistage polymerization of olefins in at least two serially connected gas-phase polymerization reactors, the process for transferring polyolefin particles from a first gas-phase polymerization reactor to a second gas-phase polymerization reactor comprising the steps of:
 a) discharging polyolefin particles from the first gas-phase polymerization reactor into a separation chamber wherein the polyolefin particles are separated from concomitantly discharged reaction gas, the separation chamber being at a lower pressure than the pressure in the first gas-phase polymerization reactor; 
 b) transferring the polyolefin particles within the separation chamber into a lower part of the separation chamber comprising a bed of polyolefin particles which moves from top to bottom of this part of the separation chamber and into which a fluid is introduced in an amount capable of producing an upward stream of the fluid in the bed of polyolefin particles above the fluid introduction point; 
 c) withdrawing polyolefin particles from the lower end of the lower part of the separation chamber and transferring the polyolefin particles to at least one lock hopper operating intermittently in parallel; and 
 d) simultaneously pressurizing one or more lock hoppers that do not comprise the polyolefin particles and operating intermittently by means of a gas comprising reaction gas coming from the second gas-phase polymerization reactor. 
 
     
     
       2. The process of  claim 1 , wherein the bed of polyolefin particles moves as plug flow from the top portion to the bottom portion of the lower part of the separation chamber. 
     
     
       3. The process of  claim 1 , wherein the lower part of the separation chamber comprising the bed of polyolefin particles comprises a conduit of a diameter smaller than the diameter of an upper part of the separation chamber. 
     
     
       4. The process of  claim 3 , wherein the conduit is arranged substantially vertically. 
     
     
       5. The process of  claim 3 , wherein the lower end of the conduit tapers conically. 
     
     
       6. The process of  claim 1 , wherein the multistage polymerization of olefins is a multistage polymerization selected from ethylene and ethylene and comonomer, wherein the polymerization in the first polymerization reactor is carried out in the presence of hydrogen. 
     
     
       7. The process of  claim 1 , wherein the fluid introduced into the conduit is an inert gas. 
     
     
       8. The process of  claim 1 , wherein the pressure in the separation chamber is in a range of from 0.12 to 0.4 MPa. 
     
     
       9. A process for polymerizing olefins according to  claim 1 , wherein one or more of the lock hoppers are optionally:
 loaded with polyolefin particles coming from the lower part of the separation chamber while the lock hopper is isolated from the second gas-phase polymerization reactor; 
 pressurized using reaction gas from the second gas-phase polymerization reactor; and 
 discharged of the polyolefin particles via transfer to the second gas-phase polymerization reactor while the lock hopper is isolated from the separation chamber.